Reactive Extrusion of Polypropylene with Pulsed Peroxide Addition: Process and Control Aspects

Controlled-rheology polypropylenes (CRPPs) have been produced by using pulsed peroxide addition during reactive extrusion of a commodity resin. It has been shown that, in contrast with processes involving continuous peroxide addition, it is possible to independently vary the weight-average molecular weight ( M̄ w ) and polydispersity (PDI). The effects of peroxide pulse characteristics on the product molecular weight characteristics have been investigated using the rheological properties of the CRPPs produced, and it has been found that the pulse width, amplitude, and period provide extra degrees of freedom for controlling M̄ w and PDI. A simple kinetic model has been employed for process simulation, and model predictions have been used to rationalize the control options through a relative gain array (RGA) analysis of the process. The results from this analysis have shown that such reactive extrusion operations are highly nonlinear and that multivariable control strategies would be required for large operating windows.